1. Field of the Invention
The present invention relates to a catalyst for use in the production of stereoregular polyolefins. More specifically, the present invention relates to a catalyst which is useful for the polymerization of olefins and comprises a specific metallocene compound which is a novel asymmetric transition metallic compound having bis-substituted-cyclopentadienyl-bridge-type bidentate ligands of bridge structure, and alumoxane.
2. Related Art
A so-called Kaminsky catalyst comprising a metallocene compound and alumoxane has been well known as a homogeneous catalyst useful for the polymerization of olefins. This catalyst is characterized in that it brings about extremely high polymerization activity, and that it can produce a polymer with a narrow molecular weight distribution.
Ethylenebis(indenyl)zirconium dichloride and ethylenebis(4,5,6,7-tetrahydroindenyl)zirconium dichloride (Japanese Patent Application Laid-Open Publication No. 130314/1986) have been known as transition metallic compounds useful for the production of isotactic polyolefins. They are, however, disadvantageous in that they produce polyolefins having low molecular weights, and that they can produce polyolefins having high molecular weights if the production is conducted at a low temperature, but, in this case, the polymerization activity is low.
Further, it has been known that a polymer having a high molecular weight can be produced when a hafnium compound is used instead of zirconium (Journal of Molecular Catalysis, 56 (1989) p. 237-247). However, this method has a shortcoming in that the polymerization activity is low.
Furthermore, dimethylsilylbis-substituted cyclopentadienylzirconium dichloride and the like are described in Japanese Patent Application Laid-Open Publication No. 301704/1989, Polymer Preprints, Japan Vol. 39, No. 6, p. 1614-1616 (1990), Japanese Patent Application Laid-Open Publication No. 12406/1991 and the like. However, there is no report concerning a catalyst which can bring about high polymerization activity and, at the same time, can give a polymer having a high molecular weight.
An object of the present invention is to provide a polymerization method by which a propylene polymer having a high molecular weight (number-average molecular weight: 70,000 or more), capable of being subjected to both extrusion molding and injection molding, can be obtained in high yield.